1. Field of the Invention
This invention relates to improvements in a fuel injection control system for an internal combustion engine, and more particularly to improvements in the fuel injection control system in which a fuel injection amount control is made depending upon an intake air flow amount detected by a hot wire mass air flow sensor.
2. Description of the Prior Art
Hitherto, a fuel injection control for an automotive internal combustion engine has been usually accomplished as follows: First, an intake air flow amount Q is detected in accordance with a signal from an air flow sensor or meter disposed in an intake air passageway of the engine. Then, a basic fuel injection amount Tp=K.times.Q/N (K=constant, N=engine speed) is calculated in accordance with the intake air flow amount Q. A variety of corrections are applied to the basic fuel injection amount Tp to obtain a final fuel injection amount Ti according to which the fuel injection control is made. In addition to such a fuel injection control, it has been proposed to prevent air-fuel mixture to be supplied to engine cylinders from becoming too rich or too lean during acceleration or deceleration by applying a compensation for time LAG (such as obtaining a moving average) on the intake air flow amount Q or the basic fuel injection amount Tp. This is disclosed in Japanese Patent Provisional Publication No. 1-290939.
In the case of using a hot wire mass air flow sensor to detect the above-mentioned intake air flow amount Q, the instant an electric power supply is made to a variety of electrical equipments in the automotive vehicle, a large amount of electric current unavoidably flows through the air flow sensor so that the air flow sensor outputs a high level (voltage) signal. It has been confirmed that there is a tendency that the intake air flow amount Q unavoidably takes a higher value than a value corresponding to an actual air flow amount when the detection of the air flow amount Q is made during such an instant.
Accordingly, if the compensation for time lug is applied to the intake air flow amount Q or the basic fuel injection amount Tp during engine starting the influence of the flow of a large amount of air unavoidably remains to a considerable extent after the engine starting where the engine starting is made immediately after the instant electric power is supplied to a variety of equipment. Additionally, owing to such an inaccurate detection of the intake air flow amount Q, there comes out a large difference in the detected air-fuel ratio of air-fuel mixture to be inducted into the engine, between a case when the engine starting is made immediately after the instant of power supply and another case when the engine starting is made a little while after the instant of power supply. This causes emsission of CO and HC (hydrocarbons) and engine speed rising behaviors to largely scatter, thereby making engine control unstable during engine starting.